Gas turbines are continuously being modified to provide increased efficiency and performance. These modifications include the ability to operate at higher temperatures and under harsher conditions, which often requires material modifications and/or coatings to protect components from such temperatures and conditions. As more modifications are introduced, additional challenges are realized.
One modification to increase performance and efficiency involves forming turbine components, such as, but not limited to shrouds, nozzles, combustion liners, buckets and shroud rings, from a ceramic matrix composite (CMC). CMC turbine components may be subject to degradation in a combustion flow field due to interactions of the CMC with combustion gases, include water, at elevated temperatures. For example, in a silicon carbide CMC, a portion of the silicon in the silicon carbide may interact with water to produce silanol species, such as silicon hydroxide, which may volatize under operating conditions in a turbine. To prevent such degradation, CMC turbine components may be protected with an environmental barrier coating (EBC). However, EBCs may be subject to spallation, particularly when subjected to high-thermo mechanical strain, such as may occur during a hard machine shutdown of a turbine, or due to foreign object damage or domestic object damage. In the event that a fragment of the EBC spalls, the CMC exposed by the loss of the EBC may again be subjected to degradation by volatilization with water.
Turbine components and methods of forming turbine components not suffering from the above drawbacks would be desirable in the art.